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The Evolution of the Anamniota

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The Evolution of the Anamniota AUSTRALIAN MUSEUM SCIENTIFIC PUBLICATIONS Leighton Kesteven, H., 1931. The evolution of the Anamniota. Records of the Australian Museum 18(4): 167–200. [21 June 1931]. doi:10.3853/j.0067-1975.18.1931.724 ISSN 0067-1975 Published by the Australian Museum, Sydney naturenature cultureculture discover discover AustralianAustralian Museum Museum science science is is freely freely accessible accessible online online at at www.australianmuseum.net.au/publications/www.australianmuseum.net.au/publications/ 66 CollegeCollege Street,Street, SydneySydney NSWNSW 2010,2010, AustraliaAustralia THE EVOLUTION OF THE ANAMNIOTA. By H. LEIGHTON KESTEVEN, D.Se., M.D., Ch.M. Bullahdelah, New South Wales. Contents. Introduction and Thesis. The Elasmobranch Age. 1. The Pregnathostomes. 2. The Evolution of the Jaws. 3. The Evolution of the Lungs. The Teleostome Age. 1. The Elasmobranchs and the Chondrostei. 2. The Crossopterygii, Dipnoi and Amphibians. 3. The Dipnoi and the Amphibians. The Evolution of the Cheiropterygium. Anomalous Structures and Resemblances. "Since the days when Gegenbauer and Thatcher and Balfour propounded their views on the origin of the limbs, vertebrate morphology has not been standing still. Great increases have been made in our knowledge. Now, in considering the working hypotheses of these earlier days of morphology, we should remember that increase in our knowledge may greatly alter our point of view, and it seems in my humble opinion that it is conducive to progress, not so much to search for new detailed facts which may bolster one or other of existing hypotheses, as to endeavour to make an impartial survey of the facts as we know them and then to consider carefully whether the body of facts so surveyed seems to suggest a working hypotheSis drawn up on the original lines or one drawn up on somewhat different lines.'" Thus, without asking his permission, I call upon Professor Graham Ken to provide an introduction to a paper on speculative morphology. That which follows is an attempt to harmonize the facts of development and adult anatomy of the Anamniota. In no case, I am well aware, would I be justified in writing Q.E.D. at the end of any section or argument. BaSing conclusions on unavoidably scanty circumstantial evidence, the student of evolu­ tion who adopts a dogmatic attitude or pOSitive language, such as that italicized by Professor Ken at the foot of page 278, betrays an unphilosophic mind or a partisan conviction. None of our working hypotheses can be proven, they are but statements of probabilities, and, as such, then, the conclusions arrived at herein are presented. My conclusions are embodied in the diagram below, so that in it I present, as it were, a thesis which it is intended to defend in the following pages. The two most radical conclusions which it is intended to convey by the diagram are: 1. The Chondrostei are bony Elasmobranchs. 2. The Dipnoi are primitive amphibians. 1 Kerr.-In, The Work of J. S. Budgett, 4to., Cambridge, 1907, pp. 277-8. E 168 RECORDS OF THE AUSTRALIAN MUSEUM. This work is founded on the study of a fairly wide range of material which includes the following: (1) a very fine series of teleostean specimens, placed at my disposal by Dr. C. Anderson, Director of the Australian Museum; (2) Chimmra and Tandanus, received from the New South Wales Fisheries Department; (3) Oallorhynchus antarctiCUS, from the Hon. G. H. Thomson of Dunedin, New Zealand; (4) Amia, Lepidosteus, and ACipenser, as well as Necturus, Pseudo­ triton, Notophthalmus and Amblystoma, through Professor W. K. Gregory, from the American Museum of Natural History; (5) a large number of Amblystoma tigrinum in alcohol and several beautiful series of sections of the head of Amphiuma, from Professors C. Judson Herrick and H. W. Norris; (6) Neoceratodu8, from Dr. T. Bancroft, Eidsvold, Queensland; (7) Psephurus, from Mr. A. De C. Sowerby, Shanghai, China; (8) Lepidosiren, through Mr. Car I P. Schmidt, from the Field Museum of Natural History, Chicago; (9) various anurous amphibians and a number of elasmobranchs collected by myself and my friends. I have to acknowledge my indebtedness to the gentlemen and institutions mentioned above and to thank them for their assistance. From this list it will be gathered that I have not been able to dissect for myself either of the recent crossopterygians, or Protopteru8, and that I have also had to rely entirely on the work of others for my knowledge of the anatomy of the gymnophiones; for the rest I have been able to study at first hand the structures of representatives of all the forms discussed? The embryological material has not been so varied: (1) sections of the head of embryonic Trout and Spar1ts; the lengths of these were not known, but they were all stages prior to the formation of bone; (2) longitudinal sections of the head, 8 mm. in length, of an unidentified shark, and well advanced as to the 2 Since this paper was finished Professor H. W. Norris placed me further in his debt by presenting me with several very fine sets of transverse sections of gymnophione heads, and I received a skull of Polypterus from Ward's Natural Science Establishment, Rochester, New York. I have also had the opportunity of working out very completely the development of the chondrocranium of the lizard Physignathus lesueurU, Gray, and that of the common fowl, as well as one stage in the development of the chondrocranium of the Frogmouth, Podargus. EXPLANATION OF THE DIAGRAM. Pregnathostomes.-The salient features of these are briefly reviewed in the text. Archignath,o'stomes.-Protovertebrata which have the first visceral arch essentially similar to the rest of the arches, but functioning at times as a jaw. The foregut has a dorsally situated glandular caecum. Neognathostomes, or Astylio Gnathostomes.-The first arch is definitely modified to act as a jaw, but is held in place, fore and aft, by fibrous unions only. A,'chistylica,.-Gnathostomes in which the maxillary arch is in cartilaginous union with the trabecula anteriorly, in the ethmoid region; probably a feature of many Pre­ and Protopulmonates. Prep1,lmonates.-Archistylic Gnathostomes in which, it is assumed, the dorsal glandular caecum of the foregut is large and fiaccid. Protopulmonat'es'.-In this stage of the evolution of the lung. it is assumed that the dorsal caecum now contains gases, but has as yet no function to perform relevant thereto. Penepulmonates.-It is assumed that now the "almost-lung" has gained control of its gaseous contents by muscular and/or glandular activity. Ap1tlmonata.-It is assumed that the caecum has become aborted. Pulmoneida.-Greek: eidos - like. The terms used at the top of the diagram are fully discussed in the text. THE EVOLUTION OF THE ANAMNIOTA-KESTEVEN. 169 NWPRO:'JENCEPMLlCA: YO.srYL..lcA· .AClrOoSry LIe",. ~okona.t Eu/> u / m on q tQ" :;i ." '.., 't ~;,; .('j ~ ~ .~ '--.j .t:i ~ ::; '" C<:l \) ~ ~ ~ ;.::; () il ~ ., " " ..; 1: ~ ~ "c: 'i:; \; ~ 1 ~ ,~ " ~ ~ ~'( ~ '-1 ~ l-{i ~ ~ ~ ~ ~ t SjOG/:.· . er A IV 0 I /). &·s;rocK:. ~ <v hnepu/mon ates. ':l Cl /1-oTopu/monoteJ'. Pl"8 jJu/m O/J er le s. For explanation see foot of preceding page: 170 RECORDS OF THE AUSTRALIAN MUSEUM. chondrocranial structures; (3) complete sets of embryos of Hyla aUl'ca, HyZa crerulca and LY1nnodynastcs peronii from the deposition of the eggs up to the appearance of the forelimbs, collected, a few each day. From these latter I have prepared sections which enable me to state that the phenomena of development of the chondrocranium is so closely similar to that described by Parker and Gaupp in Rana that I do not deem it useful to publish any further account of my findings. Though this embryo logical material is scanty, its study has enabled me to understand embryological literature and drawings as I should not have done without it. The Elasmobranch Age. 1. Thc Prcgnathostomes. Before we discuss the evolution of the fishes and amphibians it is desirable that we attempt to fOfm some idea. of the structure of the early vertebrates, pregnathostomes, from which they have evolved. We have been taught to believe that in its development each animal "climbs its own genealogical tree," and there is little reason to doubt that we have been taught aright. Now, if in our studies of embryology we find certain structural features appearing in all the vertebrates, then, even if these features be evanescent in some forms, we feel justified in concluding that the features in question were present in the common ancestor of all the forms studied. Not only is this so, but, remembering that the adult is but the last stage in the life history, we are equally justified in assuming that structures possel5sed by adult forms in common were also inherited. Two striking illustrations. Because all vertebrates al'c vertebrate, we assume a vertebrate ancestor. Because all amniotes have an amnion, we assume an amniotic ancestor for the group, distinct and different from that of the Anamniota, though, as just pointed out, tracing their ancestry further back we find that they have both sprung from a common stock. It is believed that if we sift carefully the evidence provided by the life histories and adult anatomies of the Anamniota we shall be able to arrive at the probable structure of the various ancestors as we trace backwards the converging lines of similitude. Before proceeding to an analysis of the life histories it will not be out of place to enumerate those structural features which we are all agreed must have been present in the ancestral vertebrate stock, The Archi- or Protovertebrata, pregnathostomes, were provided with a seg­ mented nervous system, whose central stem was enclosed in a more or less continuous vertebral column.
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